Abstract
This research addresses the issue of average transmit optical power reduction in multi-carrier code division multiple access (MC-CDMA)-based indoor optical wireless communications employing intensity modulation with direct detection. The problem is treated in a novel way by investigating pre- and post-equalization-based subcarrier selection for transmit power reduction in downlink transmissions. Analytical expressions are derived for upper bounds of the required fixed DC bias for both cases. The fixed DC bias is used to reduce the system complexity on one hand and to devise optimal subcarrier selection criteria on the other. Simulation results based on the proposed subcarrier selection reveal significant power reduction subject to the 10 −4 bit error rate (BER) requirement for 10-Mbps 64-subcarrier MC-CDMA-based indoor optical wireless communication systems. In addition, the BER performance obtained from pre-equalization is shown to be no higher than that obtained from post-equalization for the same transmit power.
Highlights
Multi-carrier and multiple access communication technologies like orthogonal frequency division multiple access (OFDMA) and multi-carrier code division multiple access (MC-CDMA) have captured different vistas of communications for simple text data and for different types of multimedia requiring robust transmissions
The contributions of this research, which are not reported previously to the best of the authors’ knowledge, are highlighted as follows: 1. Average transmit optical power reduction is accomplished by subcarrier selection for the first time in MC-CDMA-based indoor optical wireless communication systems employing intensity modulation with direct detection (IM/DD)
Maximal ratio combining, orthogonality restoring combining, and minimum mean square error techniques are some versions of linear equalization employed in MC-CDMA, where appropriate coefficients are used as weighting factors for the signals from different subcarriers
Summary
Multi-carrier and multiple access communication technologies like orthogonal frequency division multiple access (OFDMA) and multi-carrier code division multiple access (MC-CDMA) have captured different vistas of communications for simple text data and for different types of multimedia requiring robust transmissions. Optical wireless systems are reported to be integrated with WiFi networks to provide ubiquitous coverage systems for indoor applications [2]. In these systems, the optical spectrum provides an encouraging potential as a complementary medium to the congested radio spectrum. The optical spectrum provides an encouraging potential as a complementary medium to the congested radio spectrum For such applications, intensity modulation (IM) can be applied to either infrared or visible. Average transmit optical power reduction is accomplished by subcarrier selection for the first time in MC-CDMA-based indoor optical wireless communication systems employing intensity modulation with direct detection (IM/DD).
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